There are a number of surgical techniques for treating clouding within the eye lens, which is referred to as a cataract in medicine. The most common technique is phacoemulsification, in which a thin needle is introduced into the diseased lens and excited to vibrate by means of ultrasound. The vibrating needle emulsifies the lens in the direct vicinity thereof in such a manner that the created lens particles can be suctioned away through a line via a pump. In the process, a rinsing fluid (irrigation fluid) is supplied, with the particles and the fluid being suctioned away through an aspiration line. Once the lens has been completely emulsified and removed, a new artificial lens can be inserted into the empty capsular bag, and so a patient treated in this manner regains good visual acuity.
During emulsification, a particle can be suctioned toward the suction opening of the aspiration line in a vibrating needle in such a manner that the aspiration line is blocked. Such a state is referred to as occlusion. In this case, neither fluid nor any other broken-up lens particles can reach the aspiration line anymore. If a suction pump continues to operate in an unchanged manner, strong negative pressure builds up in the aspiration line. In general, the negative pressure does not suffice for suctioning the particles blocking the needle tip through the aspiration line. One option for terminating the occlusion is to operate the needle with higher ultrasound energy such that the particle at the needle tip breaks into smaller particles and the occlusion is terminated. However, the higher energy input for breaking up lens particles leads to the unwanted effect that the needle also strongly heats up the surrounding tissue. Since the needle is pierced through the cornea during the operation, this heats up the cornea and so the latter is also damaged (cornea burn) in the case of too long and high energy input into the eye lens. Such an injury to a patient's eye can foe avoided if the ultrasound energy required for breaking up particles is set to a low value for a relatively long period of time. However, this increases the length of the operation.